how about expressing 230 parts per thousand (ppt) of SO4^2- in mol
230 ppt is 230 g/1000 g = 230 g/kg.
Convert 230 grams into mols and you have it.
SO, I come up with an answer of 2.39 mol/kg. Correct?
calculate g/mol by writing out your molecular formula and using the atomic mass (g/mol) found on the periodic table for each element.
e.g. H20 = (2*H)+O [or H+H+O] = (2*1.007)+15.9994 = 2.014+15.9994 = 18.0134 g/mol.
230g/1000g is correct for ppt.
230g/ (calculated g/mol) = number of moles in 230g.
e.g. 230g / 18.0134g/mol = 12.7683 mol
now you have: number of moles in 230g/1000 g.
e.g. 12.7683mol / 1000g
To express ppt in mol/kg remember to convert from g to kg!